1. Field of the Invention
The present invention relates to a process for producing a flexible polyurethane foam. More particularly, the present invention relates to a process for production, employing as the blowing agent carbon dioxide which is generated by the reaction of water with free isocyanate groups, of a flexible polyurethane foam which has high elasticity and excellent extension properties, and which is useful for cushioning materials for automobiles, furniture and the like.
2. Related Background Art
Flexible polyurethane foams are used in a great quantity for cushioning materials for automobiles, furniture and the like.
For the isocyanate component for the preparation of such flexible polyurethane foams, usually used is tolylene diisocyanate solely or a mixture of tolylene diisocyanate and polyphenylmethane-polyisocyanates.
Tolylene diisocyanate and its analogues, however, involve problems in industrial hygiene because of its high vapor pressure, and are inferior in curing behavior. Further, the foams prepared therefrom have not satisfactory properties such as large compression set especially under wet and hot conditions, so that such foams are considered not to be suitable for uses like a seat-cushioning material. Under such circumstances, diphenylmethane diisocyanates have recently come to be solely utilized for production of flexible polyurethane foams.
In production of flexible polyurethane foams, water is used as a carbon-dioxide-generating agent in combination with a chlorofluorocarbon as an auxiliary blowing agent to help the blowing action of carbon dioxide. Since the use of chlorofluorocarbons has come to be severely criticized all over the world, methods are now being investigated for producing a flexible polyurethane foam by employing carbon dioxide, which is generated by the reaction of water with free isocyanate groups, as a substantially sole blowing agent. The single use of diphenylmethane diisocyanates for producing a flexible polyurethane foam involves a disadvantage that a low density foam material is not readily produced without use of auxiliary blowing agent in addition to water.
Moreover, polyetherpolyols used for flexible polyurethane foams have usually an average functionality of from 2 to 4, and an average molecular weight of from 2000 to 8000. The foams produced according to the prepolymer method by use of such a polyol have been desired to be improved further in properties of elasticity, elongation, etc.